Photographic emulsion



Oct. 14, 1958 E. c. YACKEL ET AL 2,856,283

PHOTOGRAPHIC EMULSION Filed May '7. 1956 DEVELOP/N6 AGENT- GELAT/N- SILVER HAL/DE- WAX EMULSION SUPPOR T EDWARD C. YACKEL THOMAS ABBOTT IN VEN TORS B /MW ATTORNEY 8 AGENT United States Patent 9 PHOTOGRAPHIC EMULSION Edward C. Yackel and Thomas I. Abbott, Rochester,

N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application May 7, 1956, Serial No. 583,265

7 Claims. (CI. 96-48) This invention relates to light-sensitive photographic elements and their use in certain photographic reproduction processes.

The light-sensitive element of the invention includes a gelatino-silver halide emulsion containing one or more silver halide developing agents and in addition, a substantial amount of a water-insoluble wax such as paratfin, beeswax or carnauba wax. The silver halide developing agent in the emulsion is not especially critical and is selected according to the requirements of the particular reproduction process in which the emulsion is to be used; Similarly, the quantity of wax in the emulsion is such as to adapt the sensitive element to the given process. For example, a silver halide emulsion containing gelatin, paraffin and the gelatin tanning silver halide developing agent 3,4-dihydroxydiphenyl is adapted particularly for use in the reproduction processes described in U. S. Patents 2,596,756 and 2,716,059. In those processes a substantially unhardened gelatino-silver halide emulsion containing a gelatin tanning silver halide developing agent is exposed to a subject, treated with alkaline solution to form a hardened gelatin and silver image in the region of exposure and by pressing the developed emulsion layer against an absorbent sheet, a stratum of the less exposed emulsion areas adheres to the sheet and remains on the sheet when the emulsion and sheet are separated. In those processes, when no wax is employed one condition encountered is the tendency for the unhardened stratum of emulsion to not break away cleanly from the underlying unhardened emulsion area with the result that the image obtained on the receiving sheet does not have the desired sharpeness anddefinitio n. A further difiiculty lies in the tendency for the exposed and hardened image portions of the emulsion to adhere somewhat to the receiving sheet, making separation of the emulsion and the receiving sheet more difiicult than desired.

We have discovered that if wax is incorporated into the silver halide emulsion layers used in the process of the mentioned patents, the result is that during the transfer step the substantially unhardened emulsion areas will fracture more readily when the emulsion and receiving sheet are separated, giving sharper images. Also, the mechanical separation of the emulsion from the receiving sheet is made less difficult.

Another use for the gelatino silver halide emulsions containing developing agent and wax, for example, an emulsion containing silver halide developing agent, about 13 grams of gelatin and 40 grams of wax, is in the preparation of photographic reproductions by means of a photothermographic process. The emulsion is merely exposed to a suitable subject, treated with alkaline solution to develop the silver image in the emulsion layer, then placed in intimate contact with a sheet of paper or other material absorbent of molten wax. The sandwich is then exposed to heat rays with the result that a waxen silver image is obtained on the paper underlying the ice areas of the emulsion containing the silver image. This process does not require the silver halide developingagent to be present initially in the emulsion layer and the developing step can be carried out in the presence of the developing agent using anordinary alkaline silver halide developing solution as will be described-in the examples hereinafter.

In the accompanying drawing is shown in greatly enlarged cross-sectional view, the appearance of a photo graphic element having a wax-containing emulsion layer. In the drawing, layer 10 of the element is a support such as paper or a cellulose ester film base on which is coated the emulsion layer 11 containing developing agent, gelatin, silver halide and wax such as paraflin.

Example 1 An emulsion was provided containing gelatin, silver halide, 4-phenyl catechol, 4-methoxy-1-naphthol and dispersing agent as described in U. S. Patent 2,716,059.

Fifty grams of parafiin were melted at 50 C. and added to 500 cc. of a 10 percent gelatin solution containing 50 cc. of an 8 percent aqueous saponin solution with vigorous stirring followed by running the mixture through a colloid mill.

Four kilograms of a gelatin-parafiin dispersion thus prepared were then added to the above silver halide emulsion containing 1 mole of silver halide. Before coating on a support, an equal amount of 4% aqueous gelatin solution was added.

The resulting emulsion coating containing silver halide, developing agent, gelatin'and parafiin, was then exposed by reflex printing methods to a two-tone subject so as to obtain appreciably more exposure in the highlight regions of the subject than in the shadow regions, processed with alkaline solution and a print obtained therefrom by pressing the developed emulsion layer against a paper receiving sheet. The emulsion layer and receiving sheet were then separated to obtain a direct positive image of silver, silver halide, gelatin and wax on the paper sheet. In the transfer step it Was noted that due to the presence of the wax, the emulsion layer and receiving sheet separated more readily than when a comparable emulsion free of wax was used. Also, the image could be obtained under conditions of underexposure which was not possible with the control coating not containing wax. When additional copies were made by rewetting the developed emulsion layer with the alkaline solution and again pressing against other sheets of paper, separation of the emulsion layer from the paper sheet was facilitated. 1 l

The gelatin tanning silver halide developing agents particularly useful in the wax-containing emulsions adapted to the above transfer process are:

3,4-dihydroxy diphenyl 2,5-dihydroxy diphenyl 2,3-dihydroxy diphenyl 4-phenoxy catechol 4-(2,4-di-tert. amyl) phenoxy catechol 1,2-diethoxalyl-4-phenoxy catechol In addition to the gelatin tanning silver halide developing agents, the emulsion may also contain a non-tanning silver halide developing agent such as:

4-methoxy-a-naphthol N-methyl-p-aminophenol-x-sulfonic acid p-Hydroxy-anilino-methane sulfonic acid Pyrogallol dimethyl ether S-hydroXy-u-naphthoI for the purpose set forth in U. S. Patent 2,716,059.

The gelatin of the emulsion is substantially unhardened,

that is, not substantially harder than a gelatin layer containing about 0.25 ounce of formaldehyde (40 percent formaldehyde solution diluted 1:3 with water) or 0.7 gram of dry formaldehyde per pound of gelatin when freshly.coated or 0.l ounce ofthe formaldehyde solution per pound of gelatin fora .sampleaged 3'to 6 months.

.In the above process, theformation of theimage on thereceiving sheet is facilitatedif the;sheet has been treated prior to the .transfenstep with a-silver halide fogging agent such as .thiourea, thiosemicarbazine or thioacetamide, and has also been treated with a-compoundcap able of retardinggelatin tanning such as sodium formaldehyde bisulfide, sodium formaldehyde sulfoxalate, etc,., .as :described -l]1.ih6'ChflIl et a1. U. S. Patent application Serial N0..,5,30,638, filed August ,25, 1955.

.;In the .ab,ove proees s, useful results are obtained when the emulsion contains about l part of a rwaxtsuch as paraflin per 2 parts of gelatin.

Silver halide emulsion-layers containing wax can be adapted'to usein=the mentioned thermographic process as shown in the ,followingexample.

Example 2 Forty grams ofparafiin weremelted and added to 100 cc.. of a 10 percentgelatin solution. A dispersing; agent was then added and the mixture stirred rapidly for ,2 minutes. Two parts by weight of the dispersion thus prepared were thenadded to one part of a'silverhalide emulsion containing 1 mole of silver halide and40, grams ofgelatin. The resulting emulsion was then coated onto afilmsupportand dried. The coated emulsion was exposed to a line negative, then developed with an ordinary paper. developing solution to obtain a silver image in :the exposed areas. The developed filmwas then placed with the emulsion sidein contact'with'a sheet of paper and given a heat exposure through a dark red filter to prevent exposure of theresidual silver halide. ,As a result, the emulsion in the region of the silver image melted and when the emulsion and paper were separated, animage composed of silver, gelatin and wax was obtainedon the sheet of paper.

.When the aboveprocess was carried out in thersame manner except that the emulsion layer was driedafter the development step, only a wax image transferred to the receiving sheet.

.In the above process, stearic acid can be substituted for wax andsimilar results are obtained although the procedure is less preferred.

Since the process as described in this example utilized an ordinary developing-out emulsion, a negative print was obtained with regard to the original subject. By employing a direct positive emulsion of a well-known type containing wax, a direct positive print can'be .obtained in the same manner.

The silver halide in the emulsion used in the mentioned photothermographic process is advantageously blue or green light-sensitive having little sensitivity in the infrared region to prevent exposure of the emulsion with wavelengths of light in the far red and infrared regions of the spectrum during the transfer step. Also, the process may be carried out in the'manner abovedescribed by incorporating a silver halide developing agent such as hydroquinone or the developing agents of Exam ple 1 inzthe emulsion layer together with wax, and initiating developmentwith an alkaline solution free of developing agents suoh asv dilute sodium carbonate solution.

In the described photothermographic process, useful results are obtainedwhen the emulsion contains about 3 l parts ofparafiin per 1 part of gelatin. According1y,-the emulsions useful in the processes of Examples 1 and 2 can contain about 0.5 to 3 parts of wax per part of gelatin, the emulsions containing the lower amounts of wax being preferred for the process of Example 1.

What we claim is:

1. A silver halide emulsion containing a mixture of gelatin, a silver halide developing agent, and about 0.5 to 3 parts of a Water-insoluble wax per part of gelatin.

2. A substantially unhardened silver halide emulsion containing a mixture of gelatin, about 0.5 to 3 parts of a water-insoluble waxper part of gelatin, and a silver halide developing agent of the class consisting of 3,4-dihydroxy diphenyl, 2,5-d hydroxy diphenyl, 2,3-dihydroxy diphenyl, 4-phenoxy catechol, 4-(2,4-di-tert. amyl) phenoxy catechol and 1,2-diethoxalyl-4-phenoxy catechol.

3. A photothermographic process which comprises exposing to a subject a supported emulsion layer containing amixture of gelatin, silver halidev and about 3 parts of avater-insoluble wax per -.part;gel-atin, developing the exposed emulsion layer with an alkaline solution-in'the presence-of -a-;silver halide developing agentto obtain a silver image in. theemulsion layer, placing the developed emulsion layer in contact with an absorbent. sheet and heating the emulsion layer inucontact with the absorbent sheet-for a time sufficient to transfer a wax image to the absorbent sheet.

The process ,of .claim 3 wherein the exposed emulsion layer contains a silver halide developing agent, and the development .step is carried out with an alkaline solution.

5. .Theprocess of claim -3 wherein the silver halide emulsion'is adirect positive silver halide emulsion.

- 6. A method of photographic reproduction which. comprises .exposingto ,a two-tone subject a' substantially unhardened gelatino silver halide emulsion layercontaining'a mixture of about 0.5 part of a water-insoluble wax per part of-gelatin and a developing agent of the class consisting of 3,4-dihydroxy' diphenyl, 2,5-dihydroxy diphenyl, 2,3-dihydroxy diphenyl, 4-phenoxy catechol, 4- (2,4-ditert. amyl) phenoxy catechol and ,1,2-diethoxalyl- 4-phenoxycatechol, so as to obtain some exposure in the areas of:the.en .ulsion-layer correspondingto the shadow areas oftthesubject'and appreciably more exposure in the areas .oftheemulsion layer corresponding to the highlight areas .of the ,subject, developing the exposed .emulsion layer with an alkaline solution to obtain a hardened gelatin, wax and silver image in the region of exposure'to the highlight area of the subject and substantially unhardened .gelatin, wax, silver and silver halide in the region of the emulsion layer corresponding to the shadow region-of the: subject, pressing a sheet having an absorbent surface against said emulsion layer while said emulsion layer is moist to cause only the'shadow regionof the emulsion to adhere to said sheet, and separating said sheet and emulsion layer totransferonly a stratum of said shadow region of the emulsion layer to said sheet.

7. The process of claim 6 wherein the receiving sheet has been treated prior to contact with the developed emulsion layer, with a silver halide fogging agent and a compound retarding gelatin tanning.

References Cited in the file of this patent UNITED STATES PATENTS 2,059,829 Ward Nov. 3, 1936 2,221,873 Knoefel Nov. 19, 1940 2,596,756 Yutzyet'al. May 13, 1952 2,634,677 -Klimkowski et al Apr. 14, 1953 2,691,587 Greig Oct. 12, 1954 

1. A SILVER HALIDE EMULSION CONTAINING A MIXTURE OF GELATION, A SILVER HALIDE DEVELOPING AGENT, AND ABOUT 0.5 TO 3 PARTS OF A WATER-SOLUBLE WAX PER PART OF GELATIN.
 6. A METHOD OF PHOTOGRAPHIC REPRODUCTION WHICH COMPRISES EXPOSING TO A TWO-TONE SUBJECT A SUBSTANTIALLY UNHARDENED GELATINO-SILVER HALIDE EMULSION LAYER CONTAINING A MIXTURE OF ABOUT 0.5 PART OF A WATER-INSOLUBLE WAX PER PART OF GELATIN AND A DEVELOPING AGENT OF THE CLASS CONSISTING OF 3,4-DIHYDROXY DIPHENYL, 2,5-DIHYDROXY DIPHENYL, 2,3-DIHYDROXY DIPHENYL, 4-PHENOXY CATECHOL, 4(2,4-DI-TERT. AMYL) PHENOXY CATECHOL AND 1,2-DIETHOXALYL4-PHENOXY CATECHOL, SO AS TO OBTAIN SOME EXPOSURE IN THE AREAS OF THE EMULSION LAYER CORRESPONDING TO THE SHADOW AREAS OF THE SUBJECT AND APPRECIABLY MORE EXPOSURE IN THE AREAS OF THE EMULSION LAYER CORRESPONDING TO THE HIGHLIGHT AREAS OF THE SUBJECT, DEVELOPING THE EXPOSED EMULSION LAYER WITH AN ALKALINE SOLUTION TO OBTAIN A HARDENED GELATIN, WAX AND SILVER IMAGE IN THE REGION OF EXPOSURE TO THE HIGHLIGHT AREA OF THE SUBJECT AND SUBSTANTIALLY UNHARDENED GELATIN, WAX, SILVER AND SILVER HALIDE IN THE REGION OF THE EMULSION LAYER CORRESPONDING TO THE SHADOW REGION OF THE SUBJECT, PRESSING A SHEET HAVING AN ABSORBENT SURFACE AGAINST SAID ENMULSION LAYER WHILE SAID EMULSION LAYER IS MOIST TO CAUSE ONLY THE SHADOW REGION OF THE EMULSION TO ADHERE TO SAID SHEET, AND SEPARATING SAID SHEET AND EMULSION LAYER TO TRANSFER ONLY A STRATUM OF SAID SHADOW REGION OF THE EMULSION LAYER TO SAID SHEET. 